Method for Positioning Wafers in Multiple Wafer Transport

ABSTRACT

A method for positioning wafers in dual wafer transport, includes: simultaneously moving first and second wafers placed on first and second end-effectors to positions over lift pins protruding from first and second susceptors, respectively; and correcting the positions of the first and second wafers without moving any of the lift pins relative to the respective susceptors or without moving the lift pins relative to each other, wherein when the first and second wafers are moved to the respective positions, the distance between the first wafer and tips of the lift pins of the first susceptor is substantially smaller than the distance between the second wafer and tips of the lift pins of the second susceptor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method for positioning wafers in multiple wafer transport, typically dual wafer transport, and an apparatus performing the same.

2. Description of the Related Art

In the field of CVD (Chemical Vapor Deposition) and/or ALD (Atomic Layer Deposition) apparatuses and etcher apparatuses for treating substrates such as semiconductor wafers, improvement on the productivity or throughput is one important factor. For example, U.S. Pat. No. 6,074,443 teaches a dual chamber module. However, because two wafers are simultaneously brought into the dual chamber module, centering each wafer in the dual chamber module is challenging.

SUMMARY OF THE INVENTION

Some embodiments provide a method for positioning wafers in dual wafer transport, comprising: (i) placing first and second wafers on first and second end-effectors of a fork-shaped blade of a wafer-handling robot; (ii) simultaneously moving the first and second wafers placed on the first and second end-effectors to positions over lift pins protruding from first and second susceptors, respectively; and (iii) correcting the position of the first wafer and placing the first wafer on the lift pins of the first susceptor, and then correcting the position of the second wafer and placing the second wafer on the lift pins of the second susceptor, without moving any of the lift pins relative to the respective susceptors or without moving the lift pins relative to each other, wherein when the first and second wafers are moved to the respective positions in step (ii), a distance between the first wafer and tips of the lift pins of the first susceptor is substantially smaller than a distance between the second wafer and tips of the lift pins of the second susceptor.

In some embodiments, in step (ii), a height of the lift pins protruding from the first susceptor is substantially shorter than a height of the lift pins protruding from the second susceptor.

In some embodiments, in step (ii), the first end-effector is disposed on a plane substantially lower than a plane on which the second end-effector is disposed.

In some embodiments, a method for positioning wafers in dual wafer transport, comprises: (a) placing first and second wafers on first and second end-effectors of an arm, respectively; (b) simultaneously moving the first and second wafers placed on the end-effectors to positions over lift pins protruding from first and second susceptors, respectively; (c) adjusting the position of the first wafer over the first susceptor wherein the second wafer is moved simultaneously with the first wafer as a result of the adjustment of the position of the first wafer; (d) placing the first wafer on the lift pins of the first susceptor and detaching the first wafer from the first end-effector, while maintaining the second wafer on the second end-effector; (e) adjusting the position of the second wafer over the second susceptor; (f) placing the second wafer on the lift pins of the second susceptor and detaching the second wafer from the second end-effector, while maintaining the first wafer on the lift pins of the first susceptor; (g) retracting the arm and placing the first and second wafers on the first and second susceptors, respectively.

In some embodiments, the first and second susceptors are provided in a dual wafer-processing unit, wherein the height of the first susceptor and that of the second susceptor are constantly the same. In some embodiments, the dual wafer-processing unit is a module having two process chambers with discrete and separate reaction spaces.

In some embodiments, the first and second end-effectors are disposed side by side and aligned horizontally, and in step (b), the lift pins protruding from the second susceptor are lower than are the lift pins from the first susceptor by a degree such that in step (d), when the first wafer is on the lift pins of the first susceptor, the second wafer is not in contact with the lift pins of the second susceptor. In some embodiments, in steps (d) and (f), the first and second wafers are placed on the lift pins by lowering the first and second end-effectors while the lift pins of the first and second susceptors remain unmoved. In some embodiments, in step (g), the first and second wafers are placed on the first and second susceptors by raising the first and second susceptors while the lift pins of the first and second susceptors remain unmoved.

In some embodiments, during steps (b) through (g), the lift pins of the first and second susceptors remain unmoved.

In some embodiments, the first and second end-effectors are disposed side by side and unevenly aligned in a horizontal direction, wherein the second end-effector is higher than the first end-effector by a degree such that in step (d), when the first wafer is on the lift pins of the first susceptor, the second wafer is not in contact with the lift pins of the second susceptor, wherein the height of the lift pins of the first susceptor and that of the lift pins of the second susceptor are constantly the same. In some embodiments, in steps (d) and (f), the first and second wafers are placed on the lift pins by lowering the first and second end-effectors while the lift pins of the first and second susceptors remain unmoved. In some embodiments, in step (g), the first and second wafers are placed on the first and second susceptors by raising the first and second susceptors while the lift pins of the first and second susceptors remain unmoved.

In some embodiments, the arm with the first and second end-effectors is a multi-axis robot.

In another aspect, some embodiments provide a dual wafer-processing unit comprising: first and second process chambers disposed side by side; and first and second susceptors provided in the first and second process chambers, respectively, said susceptors being capable of ascending and descending together, wherein lift pins for supporting wafers on their tips are penetrated through the first and second susceptors and are protrusible from and retractable to the first and second susceptors by the concurrent movement of the first and second susceptors relative to the first and second process chambers, while the height of the lift pins is unchanged relative to the first and second process chambers, wherein the height of the lift pins provided in the second susceptor is lower than that of the lift pins provided in the first susceptor.

In some embodiments, the first and second susceptors are movable together between an upper position for processing a wafer and a lower position for transferring a wafer, wherein when the first and second susceptors are at the lower position, the lift pins protrude from the first and second susceptors, wherein the tips of the lift pins provided in the second susceptor are lower than those of the lift pins provided in the first susceptor, and when the first and second susceptors are at the upper position, the lift pins provided in the first and second susceptors are retracted inside the first and second susceptors.

In some embodiments, the height of the lift pins provided in the second susceptor is lower than that of the lift pins provided in the first susceptor by about 5 mm to about 15 mm. In some embodiments, the first and second process chambers have discrete and separate reaction compartments. In some embodiments, the dual wafer-processing unit is a plasma CVD module.

In still another aspect, some embodiments provide a wafer-processing apparatus comprising: at least any one of the disclosed dual wafer-processing units; a wafer-handling chamber to which the dual wafer-processing unit is attached; and a wafer-handling robot for transferring wafers into the process chambers and taking out wafers from the process chambers, said wafer-handling robot being provided in the wafer-handling chamber.

For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.

FIG. 1 is a schematic plan view of a semiconductor-processing apparatus with dual chamber modules usable in some embodiments of the present invention.

FIG. 2 is a schematic plan view of a dual arm wafer-handling robot usable in some embodiments of the present invention.

FIG. 3 is a schematic cross sectional view of related parts of one chamber of a dual chamber module according to an embodiment of the present invention, wherein a susceptor is at a wafer-transfer position.

FIG. 4 is a schematic cross sectional partial view of related parts of another chamber of the dual chamber module according to an embodiment of the present invention, wherein a susceptor is at a wafer-transfer position.

FIG. 5 is a schematic plan partial view of a wafer-handling robot taking wafers into a dual chamber module (not shown).

FIG. 6 schematically illustrates wafer-positioning sequences in a dual chamber module according to a comparative method, wherein (a) a right wafer is positioned, (b) a left wafer is positioned, (c) both wafers are on lift pins, and (d) both wafers are on susceptors.

FIG. 7 schematically illustrates wafer-positioning sequences in a dual chamber module according to an embodiment of the present invention, wherein (a) a right wafer is positioned, (b) a left wafer is positioned, (c) both wafers are on lift pins, and (d) both wafers are on susceptors.

FIG. 8 schematically illustrates wafer-positioning sequences in a dual chamber module according to another embodiment of the present invention, wherein (a) a right wafer is positioned, (b) a left wafer is positioned, (c) both wafers are on lift pins, and (d) both wafers are on susceptors.

FIG. 9A is a schematic perspective view of a wafer-handling robot (showing one arm) having end-effectors at different heights according to an embodiment of the present invention. FIG. 9B and FIG. 9C are a schematic partial front view and schematic partial side view of a wafer-handling robot with two arms each having end-effectors at different heights according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid and may be constituted by a mixture of gases. In this disclosure, the reactive gas, the additive gas, and the hydrogen-containing silicon precursor may be different from each other or mutually exclusive in terms of gas types, i.e., there is no overlap of gas types among these categories. Gases can be supplied in sequence with or without overlap.

In some embodiments, “film” refers to a layer continuously extending in a direction perpendicular to a thickness direction substantially without pinholes to cover an entire target or concerned surface, or simply a layer covering a target or concerned surface. In some embodiments, “layer” refers to a structure having a certain thickness formed on a surface or a synonym of film. A film or layer may be constituted by a discrete single film or layer having certain characteristics or multiple films or layers, and a boundary between adjacent films or layers may or may not be clear and may be established based on physical, chemical, and/or any other characteristics, formation processes or sequence, and/or functions or purposes of the adjacent films or layers.

In the present disclosure where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, in the present disclosure including the examples described later, the numbers applied in specific embodiments can be modified by a range of at least ±50% in some embodiments, and the ranges applied in some embodiments may include or exclude the lower and/or upper endpoints. Further, the numbers include approximate numbers, and may refer to average, median, representative, majority, etc. in some embodiments.

In all of the disclosed embodiments, any element used in an embodiment can interchangeably or additionally be used in another embodiment unless such a replacement is not feasible or causes adverse effect or does not work for its intended purposes. Further, the present invention can equally be applied to apparatuses and methods.

In the disclosure, “substantially smaller”, “substantially different”, “substantially less” or the like may refer to a difference recognized by a skilled artisan such as those of at least 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any ranges thereof in some embodiments. Also, in the disclosure, “substantially the same”, “substantially uniform”, or the like may refer to a difference recognized by a skilled artisan such as those of less than 10%, less than 5%, less than 1%, or any ranges thereof in some embodiments.

In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

The disclosed embodiments will be explained with respect to the drawings. However, the present invention is not limited to the disclosed embodiments or the drawings.

FIG. 1 is a schematic plan view of a wafer-processing apparatus combining four process modules 1 a, 1 b, 1 c, 1 d (each provided with two reactors 2), a wafer in/out chamber 5, and a wafer-handling chamber 4 provided with back end robots 3, desirably in conjunction with controls programmed to conduct the sequences described below, which can be used in some embodiments of the present invention. In this embodiment, the wafer-processing apparatus comprises: (i) eight reactors 2 (each having a right chamber (R) and a left chamber (L)) for processing wafers on the same plane, constituting four discrete process modules (units) 1 a, 1 b, 1 c, 1 d, each module 1 having two reactors 2 arranged side by side with their fronts aligned in a line; (ii) a wafer-handling chamber 4 including two back end robots 3 (wafer-handling robots), each having at least two end-effectors accessible to the two reactors of each unit simultaneously, said wafer-handling chamber 4 having a polygonal shape having four sides corresponding to and being attached to the four process modules 1 a, 1 b, 1 c, 1 d, respectively, and one additional side for a wafer in/out chamber (load lock chamber) 5, all the sides being disposed on the same plane; and (iii) a wafer in/out chamber 5 for loading or unloading two wafers simultaneously, said wafer in/out chamber 5 being attached to the one additional side of the wafer-handling chamber, wherein each back end robot 3 is accessible to the wafer in/out chamber 5. The interior of each reactor 2 and the interior of the wafer in/out chamber 5 can be isolated from the interior of the wafer-handling chamber 4 by a gate valve 9.

In some embodiments, a controller (not shown) stores software programmed to execute sequences of wafer transfer, for example. The controller also checks the status of each process chamber, positions wafers in each process chamber using sensing systems, controls a gas box and electric box for each module, controls a front end robot (FERB) 7 in an equipment front end module (EFEM) 6 based on a distribution status of wafers stored in loading ports (LP) 8 and a load lock chamber (LLC) 5, controls back end robots (BERB) 3, and controls gate valves (GV) 9 as shown in FIG. 1. A skilled artisan will appreciate that the apparatus includes one or more controller(s) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) are communicated with the various power sources, heating systems, pumps, robotics and gas flow controllers or valves of the reactor, as will be appreciated by the skilled artisan.

In some embodiments, the apparatus has any number of process chambers greater than one (e.g., 2, 3, 4, 5, 6, or 7). In FIG. 1, the apparatus has eight process chambers, but it can have ten or more. Typically, the apparatus has one or more dual chamber modules. In some embodiments, the reactors of the modules can be any suitable reactors for processing or treating wafers, including CVD reactors such as plasma enhanced CVD reactors and thermal CVD reactors, ALD reactors such as plasma enhanced ALD reactors and thermal ALD reactors, etching reactors, UV-curing reactors. Typically, the process chambers are plasma reactors for depositing a thin film or layer on a wafer. In some embodiments, all the modules are of the same type having identical capability for treating wafers so that the unloading/loading can sequentially and regularly be timed, thereby increasing productivity or throughput. In some embodiments, the modules have different capacities (e.g., different treatments) but their handling times are substantially identical.

The apparatus disclosed in co-assigned U.S. patent application Ser. No. 13/154,271, filed Jun. 6, 2011 can be used in some embodiments, the disclosure of which is herein incorporated by reference in its entirety.

FIG. 2 is a schematic plan view of a dual-arm wafer-handling robot usable in some embodiments of the present invention. In some embodiments, this type of dual-arm wafer-handling robot can preferably be used in the apparatus illustrated in FIG. 1. However, when the number of process chambers are four or less, for example, a single-arm wafer-handling robot can be used (which is typically a multi axis robot).

As shown in FIG. 2, the robotic arm is comprised of a fork-shaped portion 22 a, a middle portion 22 b, and a bottom portion 22 c. The fork-shaped portion 22 a is equipped with end-effectors 21R and 21L for supporting wafers thereon. The fork-shaped portion 22 a and the middle portion 22 b are connected via a joint 23 a, the middle portion 22 b and the bottom portion 22 c are connected via a joint 23 b, and the bottom portion is connected to an actuator 24 via a joint 23 c. In some embodiments, any suitable wafer-handling robot can be used, such as those disclosed in U.S. Pat. No. 5,855,681, the disclosure of which is herein incorporated by reference in its entirety. In some embodiments, the robotic arm has a three-prong portion for conveying three wafers at once, instead of a fork-shaped portion.

In some embodiments, the apparatus is equipped with a wafer-positioning system or wafer-centering system. When the wafers are taken into the process chambers using a wafer-handling robot, deviations of the wafers relative to the process chambers are typically corrected by adjusting the position of the end-effectors of the wafer-handling robot before placing the wafers on susceptors in the process chambers. Although any suitable positioning methods can be employed, in some embodiments, photosensors are disposed in a wafer-handling chamber in passages of the wafers in front of gate valves between the process chambers and the wafer-handling chamber, so that the wafers block light when being carried into the process chambers. By calculating the timing of the light being blocked by the wafers, it is possible to calculate deviations of the wafers in relation to the process chambers. In some embodiments, two photosensors are used for each wafer as shown in FIG. 5. FIG. 5 is a schematic plan partial view of a wafer-handling robot taking wafers into a dual chamber module (not shown). Two wafers (W) are placed on end-effectors 51R, 51L attached to a fork-shaped portion 52. Two photosensors 53 a, 54 a are provided in the passage of the wafer on the end-effector 51R, and two photosensors 55 a, 56 a are provided in the passage of the wafer on the end-effector 51L, so that the sides of each wafer block the photosensors when being taken into the process chamber (not shown). Broken lines 53 b, 54 b, 55 b, and 56 b illustrate passages of the photosensors 53 a, 54 a, 55 a, and 56 a, respectively, relative to the wafers. The photosensors are provided in front of gate valves (not shown). Based on the timing of each light beam being blocked by the wafers, deviations of the two wafers relative to the susceptors in the process chambers can be calculated simultaneously. A skilled artisan will appreciate that the apparatus includes a controller(s) programmed or otherwise configured to cause the above detection and calculation, wherein the controller(s) will be communicated with the robotics and gas flow controllers or valves of the process chambers and the wafer-handling chamber.

In some embodiments, any suitable centering systems such as the active wafer centering (AWC) system disclosed in U.S. Pat. No. 6,990,430 and U.S. Pat. No. 7,925,378 can be employed, the disclosure of each of which is herein incorporated by reference in its entirety.

Since the positions of the two wafers on the fork-shaped portion of the robot are not changed relative to each other, even when deviations of the two wafers are calculated simultaneously, the positions of the wafers are not corrected simultaneously. Thus, the positions of the wafers are corrected one by one in the process chambers. One approach to correct the positions of the wafers is illustrated in FIG. 6. FIG. 6 schematically illustrates wafer-positioning sequences in a dual chamber module according to a comparative method. In FIG. 6( a), both a right wafer (W_(R)) on an end-effector 61R and a left wafer (W_(L)) on an end-effector 61L are placed inside respective transfer compartments of the module (the process chamber is constituted by a lower or transfer compartment and an upper or process compartment), wherein the position of the wafer W_(R) is corrected based on the deviation of the wafer calculated by a deviation calculation system such as AWC. At that time, not only the position of the wafer W_(R) but also the position of the wafer W_(L) are necessarily changed simultaneously. In FIG. 6( b), upon the correction of the position of the wafer W_(R), lift pins 63R move upward to support the wafer W_(R) and detach it from the end-effector 61R. The position of the wafer W_(L) is then corrected based on the deviation of the wafer calculated by the deviation calculation system. In FIG. 6( c), lift pins 63L move upward to support the wafer W_(L) and detach it from the end-effector 63L. In FIG. 6( d), the end-effectors 63R, 63L are retracted, and the susceptors 62R, 62L ascend to the respective process compartments of the module wherein both wafers W_(R) and W_(L) are placed on the susceptors at the respective correct positions.

However, in the above, each transfer compartment must be equipped with a mechanism for moving lift pins up and down, raising the cost of the module and the controller. Further, since the lift pins move up and down for one wafer at a time, throughput suffers.

In some embodiments, the positions of the two wafers on a fork-shaped arm are individually, separately, and consecutively corrected in respective transfer compartments above respective susceptors without moving lift pins relative to the respective susceptors or without moving lift pins relative to each other. In some embodiments, the above can be achieved by a configuration where when the first and second wafers are moved to respective positions in the process chambers, a first distance between the first wafer and tips of the lift pins of a first susceptor is substantially smaller than a second distance between the second wafer and tips of the lift pins of a second susceptor. In some embodiments, the first distance between the first wafer and the tips of the lift pins of the first susceptor is about 2 mm to about 5 mm, and the second distance between the second wafer and the tips of the lift pins of the second susceptor is about 7 mm to about 20 mm. In some embodiments, the first distance is smaller than the second distance by about 5 mm to about 15 mm (typically about 10 mm).

In some embodiments, a height of the lift pins protruding from the first susceptor is substantially shorter than a height of the lift pins protruding from the second susceptor. FIG. 7 schematically illustrates wafer-positioning sequences in a dual chamber module according to one of the above embodiments. In FIG. 7( a), both a right wafer (W_(R)) on an end-effector 71R and a left wafer (W_(L)) on an end-effector 71L are placed inside respective transfer compartments of the module (the process chamber is constituted by a lower or transfer compartment and an upper or process compartment), wherein the position of the wafer W_(R) is corrected based on the deviation of the wafer calculated by a deviation calculation system such as AWC. At that time, not only the position of the wafer W_(R) but also the position of the wafer W_(L) are necessarily changed simultaneously. In this embodiment, both lift pins 73R of a susceptor 72R and lift pins 73L of a susceptor 72L are protruded from the respective susceptors 72R, 72L where the susceptors are in the transfer compartments, and the height of the lift pins 73R is substantially greater than the height of the lift pins 73L. In FIG. 7( b), upon the correction of the position of the wafer W_(R), the end-effectors 71R, 71L move downward to support the wafer W_(R) on the lift pins 73R and detach it from the end-effector 71R. The position of the wafer W_(L) is then corrected based on the deviation of the wafer calculated by the deviation calculation system. The above operation illustrated in FIG. 7( b) is performed without moving the lift pins 73R, 73L. In FIG. 7( c), the end-effectors 71R, 71L move further downward to support the wafer W_(L) on the lift pins 73L and detach it from the end-effector 71L. The above operation illustrated in FIG. 7( c) is performed also without moving the lift pins 73R, 73L. In FIG. 7( d), the end-effectors 73R, 73L are retracted, and the susceptors 72R, 72L ascend to the respective process compartments of the module wherein both wafers W_(R) and W_(L) are placed on the susceptors at the respective correct positions. In the above, each transfer compartment omits a mechanism for moving lift pins up and down, lowering the cost of the module and the controller. Further, the lift pins do not move up and down for each positional correction of the wafers, improving throughput. In some embodiments, the height of the lift pins 73R is about 10 mm to 30 mm, and the height of the lift pins 73L is about 5 mm to about 15 mm.

In other embodiments, the first end-effector is disposed on a plane substantially lower than a plane on which the second end-effector is disposed. The above embodiments can be alternative to the embodiments illustrated in FIG. 7 or can be in combination with those illustrated in FIG. 7. FIG. 8 schematically illustrates wafer-positioning sequences in a dual chamber module according to another embodiment of the present invention. In FIG. 8( a), both a right wafer (W_(R)) on an end-effector 81R and a left wafer (W_(L)) on an end-effector 81L are placed inside respective transfer compartments of the module (the process chamber is constituted by a lower or transfer compartment and an upper or process compartment), wherein the position of the wafer W_(R) is corrected based on the deviation of the wafer calculated by a deviation calculation system such as AWC. At that time, not only the position of the wafer W_(R) but also the position of the wafer W_(L) are necessarily changed simultaneously. In this embodiment, both lift pins 83R of a susceptor 82R and lift pins 83L of a susceptor 82L are protruded from the respective susceptors 82R, 82L where the susceptors are in the transfer compartments, and the height of the lift pins 83R is substantially the same as the height of the lift pins 83L. However, the end-effector 81R is disposed on a plane substantially lower than a plane on which the end-effector 81L is disposed. In FIG. 8( b), upon the correction of the position of the wafer W_(R), the end-effectors 81R, 81L move downward to support the wafer W_(R) on the lift pins 83R and detach it from the end-effector 81R. The position of the wafer W_(L) is then corrected based on the deviation of the wafer calculated by the deviation calculation system. The above operation illustrated in FIG. 8( b) is performed without moving the lift pins 83R, 83L. In FIG. 8( c), the end-effectors 81R, 81L move further downward to support the wafer W_(L) on the lift pins 83L and detach it from the end-effector 81L. The above operation illustrated in FIG. 8( c) is performed also without moving the lift pins 83R, 83L. In FIG. 8( d), the end-effectors 83R, 83L are retracted, and the susceptors 82R, 82L ascend to the respective process compartments of the module wherein both wafers W_(R) and W_(L) are placed on the susceptors at the respective correct positions. In the above, each transfer compartment omits a mechanism for moving lift pins up and down, lowering the cost of the module and the controller. Further, the lift pins do not move up and down for each positional correction of the wafers, improving throughput. In some embodiments, the difference between the plane on which the end-effector 81R is disposed and the plane on which the end-effector 81L is disposed is about 5 mm to about 15 mm. In some embodiments, the thickness of each end-effector is about 2 mm to about 5 mm (typically about 3 mm).

FIG. 3 is a schematic cross sectional view of related parts of one chamber of a dual chamber module according to an embodiment of the present invention, wherein a susceptor is at a wafer-transfer position. The susceptor 34 is vertically movable so that a wafer on the susceptor can be moved between a lower or transfer compartment and an upper or process compartment. The susceptor 34 has holes for lift pins 31 typically at three locations. In each hole, a sheath 32 is fixedly provided, each lift pin 31 is inserted in the sheath 32 and slidable against the inner surfaces of the sheath 32. The lift pin 31 is supported on a support 32 which is attached to a bottom 35 of the process chamber. The lift pin 31 is not intended to be essentially or substantially movable although it is not necessarily fixed to the bottom 35 of the process chamber. Due to gravity and its own weight or a mechanical/magnetic mechanism, the lift pin can stay in place relative to the bottom of the process chamber. The susceptor moves up and down relative to the bottom of the process chamber and also relative to the lift pins. When the susceptor 34 moves up to the process compartment, the lift pins are completely retracted inside the susceptor, so that the wafer is no longer supported by the lift pins in the process compartment. The process compartment and the transfer compartment are divided by a separation plate 37, and when the susceptor is in the process compartment, the periphery of the susceptor 34 is surrounded by the separation plate 37. A circular duct 36 is provided around the process compartment, on which a showerhead (not shown) is placed.

FIG. 4 is a schematic cross sectional partial view of related parts of another chamber of the dual chamber module according to an embodiment of the present invention, wherein a susceptor is at a wafer-transfer position. In the other chamber (left chamber), the tips of lift pins 41 are shorter than that of the lift pins 31 in the chamber (right chamber) illustrated in FIG. 3. The lift pin 41 and a sheath 42 may be the same as the lift pin 31 and the sheath 32 of the right chamber. However, in this embodiment, a support 43 is shorter than the support 33 of the right chamber, whereby the tip of the lift pin 41 is shorter than that of the lift pin 31. In some embodiments, the lift pin 41 can be shorter than the lift pin 31, and the support 43 can be the same as the support 33. The process module constituted by the right chamber illustrated in FIG. 3 and the left chamber illustrated in FIG. 4 can be used in an operation illustrated in FIG. 7. In some embodiments, any suitable lift pins and related structures can be used, and for example, those disclosed in U.S. Pat. No. 7,638,003 can be employed, the disclosure of which is herein incorporated by reference in its entirety.

FIG. 9A is a schematic perspective view of a wafer-handling robot (showing one arm) having end-effectors at different heights according to an embodiment of the present invention, which can be used in the operation illustrated in FIG. 8. In this embodiment, an arm 93 has two prongs which has the same height, i.e., extending on the same plane. A left end effector 91L is attached to a left joint 92L, and a right end effector 91R is attached to a right joint 92R. In the above, because the left end effector 91L is attached to an upper portion of the left joint 92L, whereas the right end effector 91R is attached to a lower portion of the right joint 92R, the left and right end effectors have different heights in relation to the plane on which the two-prong arm 93 is disposed. The difference in height between the left and right end effectors may be about 5 mm to about 15 mm (typically about 5 mm to about 10 mm).

FIG. 9B and FIG. 9C are a schematic partial front view and schematic partial side view of a wafer-handling robot with two arms each having end-effectors at different heights according to an embodiment of the present invention. In this embodiment, the robot has two two-prong arms (upper arm and lower arm). As can be seen from FIGS. 9B and 9C, because a left upper end effector 91LU is attached to an upper portion of a left upper joint 92LU, whereas a right upper end effector 91RU is attached to a lower portion of a right upper joint 92RU, the left and right upper end effectors have different heights in relation to a plane on which a two-prong upper arm 93U is disposed. Likewise, because a left lower end effector 91LL is attached to an upper portion of a left lower joint 92LL, whereas a right lower end effector 91RL is attached to a lower portion of a right lower joint 92RL, the left and right lower end effectors have different heights in relation to a plane on which a two-prong lower arm 93L is disposed.

By using a robot with an arm or arms having end effectors at different heights, correction of the positions of two wafers can be accomplished without moving lift pins while correcting the positions as illustrated in FIG. 8. This embodiment can be employed in combination with any embodiments using lift pins having different heights.

It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention. 

1. A method for positioning wafers in dual wafer transport, comprising: (i) placing first and second wafers on first and second end-effectors of a fork-shaped blade of a wafer-handling robot; (ii) simultaneously moving the first and second wafers placed on the first and second end-effectors to positions over lift pins protruding from first and second susceptors, respectively; and (iii) correcting the position of the first wafer and placing the first wafer on the lift pins of the first susceptor, and then correcting the position of the second wafer and placing the second wafer on the lift pins of the second susceptor, without moving any of the lift pins relative to the respective susceptors or without moving the lift pins relative to each other, wherein when the first and second wafers are moved to the respective positions in step (ii), a distance between the first wafer and tips of the lift pins of the first susceptor is substantially smaller than a distance between the second wafer and tips of the lift pins of the second susceptor.
 2. The method according to claim 1, wherein in step (ii), a height of the lift pins protruding from the first susceptor is substantially shorter than a height of the lift pins protruding from the second susceptor.
 3. The method according to claim 1, wherein in step (ii), the first end-effector is disposed on a plane substantially lower than a plane on which the second end-effector is disposed.
 4. A method for positioning wafers in dual wafer transport, comprising: (i) placing first and second wafers on first and second end-effectors of an arm, respectively; (ii) simultaneously moving the first and second wafers placed on the end-effectors to positions over lift pins protruding from first and second susceptors, respectively; (iii) adjusting the position of the first wafer over the first susceptor wherein the second wafer is moved simultaneously with the first wafer as a result of the adjustment of the position of the first wafer; (iv) placing the first wafer on the lift pins of the first susceptor and detaching the first wafer from the first end-effector, while maintaining the second wafer on the second end-effector; (v) adjusting the position of the second wafer over the second susceptor; (vi) placing the second wafer on the lift pins of the second susceptor and detaching the second wafer from the second end-effector, while maintaining the first wafer on the lift pins of the first susceptor; (vii) retracting the arm and placing the first and second wafers on the first and second susceptors, respectively.
 5. The method according to claim 4, wherein the first and second susceptors are provided in a dual wafer-processing unit, wherein the height of the first susceptor and that of the second susceptor are constantly the same.
 6. The method according to claim 5, wherein the dual wafer-processing unit is a module having two process chambers with discrete and separate reaction spaces.
 7. The method according to claim 4, wherein the first and second end-effectors are disposed side by side and aligned horizontally, and in step (ii), the lift pins protruding from the second susceptor are lower than are the lift pins from the first susceptor by a degree such that in step (iv), when the first wafer is on the lift pins of the first susceptor, the second wafer is not in contact with the lift pins of the second susceptor.
 8. The method according to claim 7, wherein in steps (iv) and (vi), the first and second wafers are placed on the lift pins by lowering the first and second end-effectors while the lift pins of the first and second susceptors remain unmoved.
 9. The method according to claim 7, wherein in step (vii), the first and second wafers are placed on the first and second susceptors by raising the first and second susceptors while the lift pins of the first and second susceptors remain unmoved.
 10. The method according to claim 4, wherein during steps (ii) through (vii), the lift pins of the first and second susceptors remain unmoved.
 11. The method according to claim 4, wherein the first and second end-effectors are disposed side by side and unevenly aligned in a horizontal direction, wherein the second end-effector is higher than the first end-effector by a degree such that in step (iv), when the first wafer is on the lift pins of the first susceptor, the second wafer is not in contact with the lift pins of the second susceptor wherein the height of the lift pins of the first susceptor and that of the lift pins of the second susceptor are constantly the same.
 12. The method according to claim 11, wherein in steps (iv) and (vi), the first and second wafers are placed on the lift pins by lowering the first and second end-effectors while the lift pins of the first and second susceptors remain unmoved.
 13. The method according to claim 11, wherein in step (vii), the first and second wafers are placed on the first and second susceptors by raising the first and second susceptors while the lift pins of the first and second susceptors remain unmoved.
 14. The method according to claim 4, wherein the arm with the first and second end-effectors is a multi-axis robot.
 15. A dual wafer-processing unit comprising: first and second process chambers disposed side by side; and first and second susceptors provided in the first and second process chambers, respectively, said susceptors being capable of ascending and descending together, wherein lift pins for supporting wafers on their tips are penetrated through the first and second susceptors and are protrusible from and retractable to the first and second susceptors by the concurrent movement of the first and second susceptors relative to the first and second process chambers, while the height of the lift pins is unchanged relative to the first and second process chambers, wherein the height of the lift pins provided in the second susceptor is lower than that of the lift pins provided in the first susceptor.
 16. The dual wafer-processing unit according to claim 15, wherein the first and second susceptors are movable together between an upper position for processing a wafer and a lower position for transferring a wafer, wherein when the first and second susceptors are at the lower position, the lift pins protrude from the first and second susceptors, wherein the tips of the lift pins provided in the second susceptor are lower than those of the lift pins provided in the first susceptor, and when the first and second susceptors are at the upper position, the lift pins provided in the first and second susceptors are retracted inside the first and second susceptors.
 17. The dual wafer-processing unit according to claim 15, wherein the height of the lift pins provided in the second susceptor is lower than that of the lift pins provided in the first susceptor by about 5 mm to about 15 mm.
 18. The dual wafer-processing unit according to claim 15, wherein the first and second process chambers have discrete and separate reaction compartments.
 19. The dual wafer-processing unit according to claim 15, which is a plasma CVD module.
 20. A wafer-processing apparatus comprising: at least one dual wafer-processing unit of claim 15; a wafer-handling chamber to which the dual wafer-processing unit is attached; and a wafer-handling robot for transferring wafers into the process chambers and taking out wafers from the process chambers, said wafer-handling robot being provided in the wafer-handling chamber. 